1. Field of the Invention
This invention is directed to drilling rigs and to methods for erecting mobile drilling rigs.
2. Description of Related Art
The prior art discloses a variety of rigs used in drilling and various wellbore operations; for example, and not by way of limitation, U.S. Pat. Nos. 3,340,938; 3,807,109; 3,922,825; 3,942,593; 4,269,395; 4,290,495; 4,368,602; 4,489,526; 4,569,168; 4,837,992; 6,634,436; 6,523,319; and 7,306,055 and the references cited in these patents—all these patents incorporated fully herein for all purposes. The prior art discloses a variety of systems and methods for assembling and erecting a drilling rig; for example, and not by way of limitation nor as an exhaustive listing, the disclosures in U.S. Pat. Nos. 2,993,570; 3,201,091; 3,262,237; 3,749,183; 4,221,088; 4,269,009; 4,292,772; 4,305,237; 4,478,015; 4,587,778; 4,630,425; and 4,932,175.
Often drilling rigs and related systems, structures, equipment, and apparatuses are delivered to a site, assembled, raised, disassembled, and transported to a new site. It is important that drilling rigs and their components be easily transported, assembled, and erected.
In many prior rigs and erection methods, rig components and structures used with a rig are raised by a crane and positioned on a rig's drill floor. Various problems and disadvantages are associated with using a crane. A crane is typically a large apparatus which is transported to a drilling site where it is assembled and/or made ready for lifting and locating rig components.